From Benign to Fulminant: Clinical Features and Fatal Outcomes of Influenza-Associated Encephalitis in Children

Purpose: Influenza-associated encephalitis/encephalopathy (IAE) in children ranges from a mild, self-limited illness to rapidly fatal neurological deterioration. This study investigated the clinical features, treatment timing, and risk factors associated with mortality and unfavorable neurological outcomes in pediatric IAE.Methods: This retrospective study included 17 children diagnosed with IAE at a tertiary center between October 2025 and February 2026. IAE was defined by laboratory-confirmed influenza infection and clinical criteria for encephalitis after alternative etiologies had been excluded. Patients were categorized into three outcome groups: full recovery, mild-to-moderate sequelae, and mortality. Clinical characteristics were compared among the three groups and analyzed to identify potential risk factors associated with adverse neurological outcomes.Results: Among the 17 patients (median age, 8.1 years), 10 recovered fully, four developed sequelae, and three died. Vaccination history differed significantly among the outcome groups (P=0.011); none of the patients who died had received influenza vaccination for at least 2 years before admission. Two fatal cases deteriorated abruptly within 12 hours after presentation and died before treatment could be initiated. The treatment interval differed significantly among the groups (P=0.003). In multivariable Firth models, treatment within 24 hours and prior vaccination showed protective trends, whereas brainstem involvement on magnetic resonance imaging and ventilator support were associated with increased odds of mortality; however, statistical significance was not reached.Conclusion: Although many children with IAE recover completely, the disease can progress rapidly to fatal outcomes in a subset of patients. Prompt recognition, early treatment initiation, and prior influenza vaccination may reduce the risk of severe neurological complications.